U.S. patent application number 13/620741 was filed with the patent office on 2013-01-10 for x-mimo systems with multi-transmitters and multi-receivers.
This patent application is currently assigned to Research In Motion Limited. Invention is credited to Mohammadhadi Baligh, Ming Jia, Amir Khandani, Jianglei Ma, Mohammad Ali Maddah-Ali, Seyed Abolfazi Motahari, Wen Tong, Peiying Zhu.
Application Number | 20130010840 13/620741 |
Document ID | / |
Family ID | 45564823 |
Filed Date | 2013-01-10 |
United States Patent
Application |
20130010840 |
Kind Code |
A1 |
Maddah-Ali; Mohammad Ali ;
et al. |
January 10, 2013 |
X-MIMO Systems with Multi-Transmitters and Multi-Receivers
Abstract
A method and apparatus for transmitting and receiving a wireless
transmission of a plurality of data streams in a wireless
communication system having a plurality of nodes is disclosed. Each
node has multiple antennas. The method involves receiving first and
second data streams from respective first and second nodes at a
receiver node, causing the receiver node to generate a receive
filter for decoding each of the received data streams, and causing
the receiver node to transmit receive filter information for each
of the first and second data streams, the receive filter
information facilitating precoding of the first and second data
streams for simultaneous transmission within a common frequency
band to the receiver node.
Inventors: |
Maddah-Ali; Mohammad Ali;
(Piscataway, NJ) ; Motahari; Seyed Abolfazi;
(Kitchener, CA) ; Khandani; Amir; (Kitchener,
CA) ; Baligh; Mohammadhadi; (Kanata, CA) ;
Jia; Ming; (Ottawa, CA) ; Ma; Jianglei;
(Kanata, CA) ; Zhu; Peiying; (Kanata, CA) ;
Tong; Wen; (Ottawa, CA) |
Assignee: |
Research In Motion Limited
Waterloo
CA
|
Family ID: |
45564823 |
Appl. No.: |
13/620741 |
Filed: |
September 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12806209 |
Sep 24, 2009 |
|
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13620741 |
|
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61100118 |
Sep 25, 2008 |
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Current U.S.
Class: |
375/211 |
Current CPC
Class: |
H04L 25/0204 20130101;
H04L 25/0232 20130101; H04L 5/0007 20130101; H04L 25/03343
20130101 |
Class at
Publication: |
375/211 |
International
Class: |
H04B 7/15 20060101
H04B007/15 |
Claims
1. For use in a wireless communication system having a plurality of
nodes, each node having multiple antennas, a relay station
configured to: receive first and second data streams from
respective first and second nodes; generate a receive filter for
decoding each of said first and second data streams; and transmit
receive filter information for each of said first and second data
streams, said receive filter information facilitating precoding of
simultaneous transmissions within a common frequency band to said
relay station.
2. The relay station of claim 1, wherein the receive filter
comprises a minimum mean squared error filter.
3. The relay station of claim 1, wherein the receive filter
comprises a zero forcing filter.
4. The relay station of claim 1, wherein the wireless communication
system is a Long Term Evolution (LTE) system.
5. The relay station of claim 1, wherein the receive filter
information for each of said first and second data streams is
associated with a compound filter.
6. The relay station of claim 1, wherein the first and second data
streams include pilot signals.
7. The relay station of claim 6, wherein each filter is generated
based on the pilot signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
patent application 61/100,118, filed on Sep. 25, 2008.
MICROFICHE APPENDIX
[0002] Not applicable.
TECHNICAL FIELD
[0003] This application relates to wireless communication
techniques in general, and to a techniques of the present
disclosure, in particular.
SUMMARY
[0004] Aspects and features of the present application will become
apparent to those ordinarily skilled in the art upon review of the
following description of specific embodiments of the disclosure in
conjunction with the accompanying drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Embodiments of the present application will now be
described, by way of example only, with reference to the
accompanying drawing figures, wherein:
[0006] FIG. 1 is a block diagram of a cellular communication
system;
[0007] FIG. 2 is a block diagram of an example base station that
might be used to implement some embodiments of the present 5
application;
[0008] FIG. 3 is a block diagram of an example wireless terminal
that might be used to implement some embodiments of the present
application;
[0009] FIG. 4 is a block diagram of an example relay station that
might be used to implement some embodiments of the present
application;
[0010] FIG. 5 is a block diagram of a logical breakdown of an
example OFDM transmitter architecture that might be used to
implement some embodiments of the present application;
[0011] FIG. 6 is a block diagram of a logical breakdown of an
example OFDM receiver architecture that might be used to implement
some embodiments of the present application;
[0012] FIG. 7(a) is an example SC-FDMA transmitter for single-in
single-out (SISO) configuration provided in accordance with one
embodiment of the present application;
[0013] FIG. 7(b) is an example SC-1-DMA receiver for SISO
configuration provided in accordance with the embodiment of FIG.
7(a);
[0014] FIG. 8 illustrates NB-NB cooperation;
[0015] FIG. 9 illustrates NB-relay cooperation;
[0016] FIG. 10 illustrates relay-relay cooperation;
[0017] FIG. 11 illustrates a multi-access channel or uplink
system;
[0018] FIG. 12 illustrates a broadcast channel or down-link
system;
[0019] FIG. 13 illustrates an interference channel or concurrent
point-to-point communication system;
[0020] FIG. 14 illustrates a proposed scheme;
[0021] FIG. 15 illustrates a basic configuration for two
transmitters and two receivers;
[0022] FIG. 16 illustrates an application of the proposed scheme in
MIMO downlink with parallel relays;
[0023] FIG. 17 illustrates an application of the proposed scheme in
MIMO uplink with parallel relays;
[0024] FIG. 18 illustrates an application of the proposed scheme in
MIMO interference channels with parallel relays;
[0025] FIG. 19 illustrates an example for signaling scheme for the
proposed scenario based on zero-forcing scheme;
[0026] FIG. 20 illustrates multipoint-to-point and
point-to-multipoint communication;
[0027] FIG. 21 illustrates interference channel or concurrent
point-to-point and X-MIMO;
[0028] FIG. 22 illustrates an application in downlink with parallel
relays;
[0029] FIG. 23 illustrates an application in uplink with parallel
relays; and
[0030] FIG. 24 illustrates an application in interference channels
with parallel relays.
[0031] Like reference numerals are used in different figures to
denote similar elements.
DETAILED DESCRIPTION OF THE DRAWINGS WIRELESS SYSTEM OVERVIEW
[0032] Referring to the drawings, FIG. 1 shows a base station
controller (BSC) 10 which controls wireless communications within
multiple cells 12, which cells are served by corresponding base
stations (BS) 14. In some configurations, each cell is further
divided into multiple sectors 13 or zones (not shown), In general,
each base station 14 facilitates communications using OFDM with
mobile and/or wireless terminals 16, which are within the cell 12
associated with the corresponding base station 14. The movement of
the mobile terminals 16 in relation to the base stations 14 results
in significant fluctuation in channel conditions. As illustrated,
the base stations 14 and mobile terminals 16 may include multiple
antennas to provide spatial diversity for communications. In some
configurations, relay stations 15 may assist in communications
between base stations 14 and wireless terminals 16, Wireless
terminals 16 can be handed off 18 from any cell 12, sector 13, zone
(not shown), base station 14 or relay 15 to an other cell 12,
sector 13, zone (not shown), base station 14 or relay 15. In some
configurations, base stations 14 communicate with each and with
another network (such as a core network or the internet, both not
shown) over a backhaul network 11. In some configurations, a base
station controller 10 is not needed.
[0033] With reference to FIG. 2, an example of a base station 14 is
illustrated. The base station 14 generally includes a control
system 20, a baseband processor 22, transmit circuitry 24, receive
circuitry 26, multiple antennas 28, and a network interface 30. The
receive circuitry 26 receives radio frequency signals bearing
information from one or more remote transmitters provided by mobile
terminals 16 (illustrated in FIG. 3) and relay stations 15
(illustrated in FIG. 4). A low noise amplifier and a filter (not
shown) may cooperate to amplify and remove broadband interference
from the signal for processing. Downconversion and digitization
circuitry (not shown) will then downconvert the filtered, received
signal to an intermediate or baseband frequency signal, which is
then digitized into one or more digital streams.
[0034] The baseband processor 22 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. As such, the baseband
processor 22 is generally implemented in one or more digital signal
processors (DSPs) or application-specific integrated circuits
(ASICs). The received information is then sent across a wireless
network via the network interface 30 or transmitted to another
mobile terminal 16 serviced by the base station 14, either directly
or with the assistance of a relay 15.
[0035] On the transmit side, the baseband processor 22 receives
digitized data, which may represent voice, data, or control
information, from the network interface 30 under the control of
control system 20, and encodes the data for transmission. The
encoded data is output to the transmit circuitry 24, where it is
modulated by one or more carrier signals having a desired transmit
frequency or frequencies. A power amplifier (not shown) will
amplify the modulated carrier signals to a level appropriate for
transmission, and deliver the modulated carrier signals to the
antennas 28 through a matching network (not shown). Modulation and
processing details are described in greater detail below.
[0036] With reference to FIG. 3, an example of a mobile terminal 16
is illustrated. Similarly to the base station 14, the mobile
terminal 16 will include a control system 32, a baseband processor
34, transmit circuitry 36, receive circuitry 38, multiple antennas
40, and user interface circuitry 42. The receive circuitry 38
receives radio frequency signals bearing information from one or
more base stations 14 and relays 15. A low noise amplifier and a
filter (not shown) may cooperate to amplify and remove broadband
interference from the signal for processing. Downconversion and
digitization circuitry (not shown) will then downconvert the
filtered, received signal to an intermediate or baseband frequency
signal, which is then digitized into one or more digital
streams.
[0037] The baseband processor 34 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. The baseband processor
34 is generally implemented in one or more digital signal
processors (DSPs) and application specific integrated circuits
(ASICs).
[0038] For transmission, the baseband processor 34 receives
digitized data, which may represent voice, video, data, or control
information, from the control system 32, which it encodes for
transmission. The encoded data is output to the transmit circuitry
36, where it is used by a modulator to modulate one or more carrier
signals that is at a desired transmit frequency or frequencies. A
power amplifier (not shown) will amplify the modulated carrier
signals to a level appropriate for transmission, and deliver the
modulated carrier signal to the antennas 40 through a matching
network (not shown). Various modulation and processing techniques
available to those skilled in the art are used for signal
transmission between the mobile terminal and the base station,
either directly or via the relay station,
[0039] In OFDM modulation, the transmission band is divided into
multiple, orthogonal carrier waves. Each carrier wave is modulated
according to the digital data to be transmitted. Because OFDM
divides the transmission band into multiple carriers, the bandwidth
per carrier decreases and the modulation time per carrier
increases. Since the multiple carriers are transmitted in parallel,
the transmission rate for the digital data, or symbols, on any
given carrier is lower than when a single carrier is used.
[0040] OFDM modulation utilizes the performance of an Inverse Fast
Fourier Transform (IFFT) on the information to be transmitted. For
demodulation, the performance of a Fast
[0041] Fourier Transform (FFT) on the received signal recovers the
transmitted information. In practice, the IFFT and FFT are
provided, by digital signal processing carrying out an Inverse
Discrete Fourier Transform (IDFT) and Discrete Fourier Transform
(DFT), respectively. Accordingly, the characterizing feature of
OFDM modulation is that orthogonal carrier waves are generated for
multiple bands within a transmission channel. The modulated signals
are digital signals having a relatively low transmission rate and
capable of staying within their respective bands. The individual
carrier waves are not modulated directly by the digital signals.
Instead, all carrier waves are modulated at once by IFFT
processing,
[0042] In operation, OFDM is preferably used for at least downlink
transmission from the base stations 14 to the mobile terminals 16.
Each base station 14 is equipped with "n" transmit antennas 28
(n>=1), and each mobile terminal 16 is equipped with "m" receive
antennas 40 (m>=1). Notably, the respective antennas can be used
for reception and transmission using appropriate duplexers or
switches and are so labeled only for clarity.
[0043] When relay stations 15 are used, OFDM is preferably used for
downlink transmission from the base stations 14 to the relays 15
and from relay stations 15 to the mobile terminals 16.
[0044] With reference to FIG. 4, an example of a relay station 15
is illustrated. Similarly to the base station 14, and the mobile
terminal 16, the relay station 15 will include a control system
132, a baseband processor 134, transmit circuitry 136, receive
circuitry 138, multiple antennas 130, and relay circuitry 142, The
relay circuitry 142 enables the relay 14 to assist in
communications between a base station 16 and mobile terminals 16.
The receive circuitry 138 receives radio frequency signals bearing
information from one or more base stations 14 and mobile terminals
16. A low noise amplifier and a filter (not shown) may cooperate to
amplify and remove broadband interference from the signal for
processing. Downconversion and digitization circuitry (not shown)
will then downconvert the filtered, received signal to an
intermediate or baseband frequency signal, which is then digitized
into one or more digital streams.
[0045] The baseband processor 134 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. The baseband processor
134 is generally implemented in one or more digital signal
processors (DSPs) and application specific integrated circuits
(ASICs).
[0046] For transmission, the baseband processor 134 receives
digitized data, which may represent voice, video, data, or control
information, from the control system 132, which it encodes for
transmission. The encoded data is output to the transmit circuitry
136, where it is used by a modulator to modulate one or more
carrier signals that is at a desired transmit frequency or
frequencies. A power amplifier (not shown) will amplify the
modulated carrier signals to a level appropriate for transmission,
and deliver the modulated carrier signal to the antennas 130
through a matching network (not shown). Various modulation and
processing techniques available to those skilled in the art are
used for signal transmission between the mobile terminal and the
base station, either directly or indirectly via a relay station, as
described above.
[0047] With reference to FIG. 5, a logical OFDM transmission
architecture will be described. Initially, the base station
controller 10 will send data to be transmitted to various mobile
terminals 16 to the base station 14, either directly or with the
assistance of a relay station 15. The base station 14 may use the
channel quality indicators (CQIs) associated with the mobile
terminals to schedule the data for transmission as well as select
appropriate coding and modulation for transmitting the scheduled
data. The CQIs may be directly from the mobile terminals 16 or
determined at the base station 14 based on information provided by
the mobile terminals 16. In either case, the CQI for each mobile
terminal 16 is a function of the degree to which the channel
amplitude (or response) varies across the OFDM frequency band.
[0048] Scheduled data 44, which is a stream of bits, is scrambled
in a manner reducing the peak-to-average power ratio associated
with the data using data scrambling logic 46. A cyclic redundancy
check (CRC) for the scrambled data is determined and appended to
the scrambled data using CRC adding logic 48. Next, channel coding
is performed using channel encoder logic 50 to effectively add
redundancy to the data to facilitate recovery and error correction
at the mobile terminal 16. Again, the channel coding for a
particular mobile terminal 16 is based on the CQI. In some
implementations, the channel encoder logic 50 uses known Turbo
encoding techniques. The encoded data is then processed by rate
matching logic 52 to compensate for the data expansion associated
with encoding.
[0049] Bit interleaver logic 54 systematically reorders the bits in
the encoded data to minimize the loss of consecutive data bits. The
resultant data bits are systematically mapped into corresponding
symbols depending on the chosen baseband modulation by mapping
logic 56. Preferably, Quadrature Amplitude Modulation (QAM) or
Quadrature Phase Shift Key (QPSK) modulation is used. The degree of
modulation is preferably chosen based on the CQI for the particular
mobile terminal. The symbols may be systematically reordered to
further bolster the immunity of the transmitted signal to periodic
data loss caused by frequency selective fading using symbol
interleaver logic 58.
[0050] At this point, groups of bits have been mapped into symbols
representing locations in an amplitude and phase constellation.
When spatial diversity is desired, blocks of symbols are then
processed by space-time block code (STC) encoder logic 60, which
modifies the symbols in a fashion making the transmitted signals
more resistant to interference and more readily decoded at a mobile
terminal 16, The STC encoder logic 60 will process the incoming
symbols and provide "n" outputs corresponding to the number of
transmit antennas 28 for the base station 14. The control system 20
and/or baseband processor 22 as described above with respect to
FIG. 5 will provide a mapping control signal to control STC
encoding. At this point, assume the symbols for the "n" outputs are
representative of the data to be transmitted and capable of being
recovered by the mobile terminal 16.
[0051] For the present example, assume the base station 14 has two
antennas 28 (n=2) and the STC encoder logic 60 provides two output
streams of symbols. Accordingly, each of the symbol streams output
by the STC encoder logic 60 is sent to a corresponding IFFT
processor 62, illustrated separately for ease of understanding.
Those skilled in the art will recognize that one or more processors
may be used to provide such digital signal processing, alone or in
combination with other processing described herein. The IFFT
processors 62 will preferably operate on the respective symbols to
provide an inverse Fourier Transform. The output of the
[0052] IFFT processors 62 provides symbols in the time domain. The
time domain symbols are grouped into frames, which are associated
with a prefix by prefix insertion logic 64. Each of the resultant
signals is up-converted in the digital domain to an intermediate
frequency and converted to an analog signal via the corresponding
digital up-conversion (DUC) and digital-to-analog (D/A) conversion
circuitry 66. The resultant (analog) signals are then
simultaneously modulated at the desired RF frequency, amplified,
and transmitted via the RF circuitry 68 and antennas 28. Notably,
pilot signals known by the intended mobile terminal 16 are
scattered among the sub-carriers. The mobile terminal 16, which is
discussed in detail below, will use the pilot signals for channel
estimation.
[0053] Reference is now made to FIG. 6 to illustrate reception of
the transmitted signals by a mobile terminal 16, either directly
from base station 14 or with the assistance of relay 15. Upon
arrival of the transmitted signals at each of the antennas 40 of
the mobile terminal 16, the respective signals are demodulated and
amplified by corresponding RF circuitry 70. For the sake of
conciseness and clarity, only one of the two receive paths is
described and illustrated in detail. Analog-to-digital (A/D)
converter and down-conversion circuitry 72 digitizes and
downconverts the analog signal for digital processing. The
resultant digitized signal may be used by automatic gain control
circuitry (AGC) 74 to control the gain of the amplifiers in the RF
circuitry 70 based on the received signal level.
[0054] Initially, the digitized signal is provided to
synchronization logic 76, which includes coarse synchronization
logic 78, which buffers several OFDM symbols and calculates an
auto-correlation between the two successive OFDM symbols. A
resultant time index corresponding to the maximum of the
correlation result determines a fine synchronization search window,
which is used by fine synchronization logic 80 to determine a
precise framing starting position based on the headers. The output
of the fine synchronization logic 80 facilitates frame acquisition
by frame alignment logic 84. Proper framing alignment is important
so that subsequent FFT processing provides an accurate conversion
from the time domain to the frequency domain. The fine
synchronization algorithm is based on the correlation between the
received pilot signals carried by the headers and a local copy of
the known pilot data. Once frame alignment acquisition occurs, the
prefix of the OFDM symbol is removed with prefix removal logic 86
and resultant samples are sent to frequency offset correction logic
88, which compensates for the system frequency offset caused by the
unmatched local oscillators in the transmitter and the receiver.
Preferably, the synchronization logic 76 includes frequency offset
and clock estimation logic 82, which is based on the headers to
help estimate such effects on the transmitted signal and provide
those estimations to the correction logic 88 to properly process
OFDM symbols.
[0055] At this point, the OFDM symbols in the time domain are ready
for conversion to the frequency domain using FFT processing logic
90. The results are frequency domain symbols, which are sent to
processing logic 92. The processing logic 92 extracts the scattered
pilot signal using scattered pilot extraction logic 94, determines
a channel estimate based on the extracted pilot signal using
channel estimation logic 96, and provides channel responses for all
sub-carriers using channel reconstruction logic 98. In order to
determine a channel response for each of the sub-carriers, the
pilot signal is essentially multiple pilot symbols that are
scattered among the data symbols throughout the OFDM sub-carriers
in a known pattern in both time and frequency. Continuing with FIG.
6, the processing logic compares the received pilot symbols with
the pilot symbols that are expected in certain sub-carriers at
certain times to determine a channel response for the sub-carriers
in which pilot symbols were transmitted. The results are
interpolated to estimate a channel response for most, if not all,
of the remaining sub-carriers for which pilot symbols were not
provided. The actual and interpolated channel responses are used to
estimate an overall channel response, which includes the channel
responses for most, if not all, of the sub-carriers in the OFDM
channel.
[0056] The frequency domain symbols and channel reconstruction
information, which are derived from the channel responses for each
receive path are provided to an STC decoder 100, which provides STC
decoding on both received paths to recover the transmitted symbols.
The channel reconstruction information provides equalization
information to the STC decoder 100 sufficient to remove the effects
of the transmission channel when processing the respective
frequency domain symbols.
[0057] The recovered symbols are placed back in order using symbol
de-interleaver logic 102, which corresponds to the symbol
interleaver logic 58 of the transmitter. The deinterleaved symbols
are then demodulated or de-mapped to a corresponding bitstream
using de-mapping logic 104. The bits are then de-interleaved using
bit de-interleaver logic 106, which corresponds to the bit
interleaver logic 54 of the transmitter architecture. The
deinterleaved bits are then processed by rate de-matching logic 108
and presented to channel decoder logic 110 to recover the initially
scrambled data and the CRC checksum. Accordingly, CRC logic 112
removes the CRC checksum, checks the scrambled data in traditional
fashion, and provides it to the de-scrambling logic 114 for
de-scrambling using the known base station de-scrambling code to
recover the originally transmitted data 116.
[0058] In parallel to recovering the data 116, a CQI, or at least
information sufficient to create a CQI at the base station 14, is
determined and transmitted to the base station 14. As noted above,
the CQI may be a function of the carrier-to-interference ratio
(CR), as well as the degree to which the channel response varies
across the various sub-carriers in the OFDM frequency band. For
this embodiment, the channel gain for each sub-carrier in the OFDM
frequency band being used to transmit information is compared
relative to one another to determine the degree to which the
channel gain varies across the OFDM frequency band. Although
numerous techniques are available to measure the degree of
variation, one technique is to calculate the standard deviation of
the channel gain for each sub-carrier throughout the OFDM frequency
band being used to transmit data.
[0059] Referring to FIG. 7, an example SC-FDMA transmitter 7(a) and
receiver 7(b) for single-in single-out (SISO) configuration is
illustrated provided in accordance with one embodiment of the
present application. In SISO, mobile stations transmit on one
antenna and base stations and/or relay stations receive on one
antenna, FIG. 7 illustrates the basic signal processing steps
needed at the transmitter and receiver for the LTE SC-FDMA uplink.
In some embodiments, SC-FDMA (Single-Carrier Frequency Division
Multiple Access) is used. SC-FDMA is a modulation and multiple
access scheme introduced for the uplink of 3GPP Long Term Evolution
(LTE) broadband wireless fourth generation (4G) air interface
standards, and the like. SC-FDMA can be viewed as a DFT pre-coded
OFDMA scheme, or, it can be viewed as a single carrier (SC)
multiple access scheme. There are several similarities in the
overall transceiver processing of SC-FDMA and OFDMA. Those common
aspects between OFDMA and SC-FDMA are illustrated in the OFDMA
TRANSMIT CIRCUITRY and OFDMA RECEIVE CIRCUITRY, as they would be
obvious to a person having ordinary skill in the art in view of the
present specification. SC-FDMA is distinctly different from OFDMA
because of the DFT pre-coding of the modulated symbols, and the
corresponding IDFT of the demodulated symbols. Because of this
pre-coding, the SC-FDMA sub-carriers are not independently
modulated as in the case of the OFDMA sub-carriers. As a result,
PAPR of SC-FDMA signal is lower than the PAPR of OFDMA signal.
Lower PAPR greatly benefits the mobile terminal in terms of
transmit power efficiency.
[0060] FIGS. 1 to 7 provide one specific example of a communication
system that could be used to implement embodiments of the
application. It is to be understood that embodiments of the
application can be implemented with communications systems having
architectures that are different than the specific example, but
that operate in a manner consistent with the implementation of the
embodiments as described herein.
[0061] Further details of embodiments of aspects of the present
application are provided below.
[0062] The above-described and below-described embodiments of the
present application are intended to be examples only. Those of
skill in the art may effect alterations, modifications and
variations to the particular embodiments without departing from the
scope of the application.
Keywords for Searching:
[0063] MIMO
[0064] Multiple transmit and multiple receive antennas
[0065] Multiple transmitters and multiple receivers
[0066] Spatial multiplexing
[0067] Multi-user MIMO
[0068] Non-cooperative communications
[0069] Spectrum Sharing
[0070] Parallel relaying
[0071] Interference management
[0072] Network coding
[0073] Sofr handover
[0074] Mesh networking
[0075] Self-organized networks
[0076] WiFi
[0077] GiFi
[0078] Gigabit MIMO
[0079] Products that will use this Application:
[0080] Potoentially extendable to WiMAX and LTE
[0081] IEEE802.16m
[0082] IEEE802.11n
[0083] IEEE802.11VHT
[0084] IEEE802.15
[0085] Beyond 4G systems
[0086] IMT-advanced systems
[0087] Is this Application relevant to a Standards Activity?
yes
[0088] If so, give details:
[0089] Plan to develop the next generation standard based on this
concept
[0090] Especially IEEE802.16m and LTE-Advanced
TECHNICAL INFORMATION
[0091] Brief Description of the Application:
[0092] This Application configures more than one multi-antenna
transmitter and more than one multi-antenna-receiver, each
transmitter has the knowledge of the MIMO channels information and
there is NO data-exchanging required between the transmitters (non
cooperative transmission), there is NO data-exchanging in the
receiver side. Linear pre-coding can be applied at transmitters
and/or receivers. The transmit and receive per-coding/filtering is
performed such that the dimension of the interference is minimized.
This is core value of this Application, since we can minimized the
number of transmit/receive antennas to achieve highest spectral
efficiency, as an example, if we have 2 users each with 2
transmits, in the conventional receiver requires 4 receive antennas
for each user in order to achieve multiplexing again of 4, with
this Application, we only need 3 receive antennas for each user to
achieve the same multiplexing again of 4 without penalty on the
transmit power and bandwidth, this architecture is called X-MIMO.
The basic scheme of X-MIMO can be generalized to many
wireless/wireline appellation, such as multi-hop relay, total
distributed MIMO networking.
[0093] Problem Solved by the Application:
[0094] This Application provides solutions for the following
fundamental difficulties in distributed broadband wireless
networking: e.g. (1) achieving the higher multiplexing gain without
exchange the data at both transmitter side and receiver side, which
no prior arts can do this, this is a major obstacle to enable
disturbed multi-user communications (2) this scheme enable the
relay node sharing between the multiple data path to support
distinct source-destination routing, for example in MIMO downlink
system, where more than one relay nodes and more than one receivers
(3) to achieving a give multiplexing gain, this solution requires
minimum number of transmit/receive antennas or (4) with the given
number of transmit/receive antenna, this scheme achieve the maximum
multiplexing gain.
[0095] Solutions that have been tried and why they didn't work:
[0096] Two high cost alternative solutions to achieve the same
performance are (1) Using an additional backbone system to connect
transmitters or receivers which enable us to apply advance schemes
such as dirty paper precoding (2) Using more than transmit/receive
antennas.
[0097] For the first alternative, in many practical case the
connections between transmits or receivers are not possible, for
the second alternative, additional more antennas will be limited by
the device form factor, both solutions are expensive.
[0098] Specific elements or steps that solved the problem and how
they do it:
[0099] The basic elements of this Application are several
multi-antenna transmitters and several multi-antenna receivers and
associated pilots. The operational steps are the followings:
[0100] [1] Each transmitter sends the pilot for each antenna and
the pilot for each transmitter is orthogonal.
[0101] [2] Each receiver estimates all the incoming MIMO channels
and compute the specific receive filters and each receiver feeds
back the compound filter and MIMO channel to via dedicated feedback
channel to a specific transmitter
[0102] [3] Each transmitter computes the linear pre-coding filter
based on such feedback information from the receiver
[0103] [4] Each transmitter sends the pre-coded data
[0104] [5] Each receiver demodulates the corresponding data from
filtered receive signal
[0105] Commercial Value of the Application to Nortel and Nortel's
Major Competitors:
[0106] This Application can be used as Nortel-specific proparteiry
implementation or it can be standardized in the next generation
broadband wireless standards.
TABLE-US-00001 3GPP TSG-Ran Working Group 1 Meeting #54b R1-083870
Prague, Czech Republic, Sep. 29.sup.th-Oct. 3.sup.rd, 2008 Agenda
Item: 11 Source: Nortel Title: LTE-A Downlink Multi-site MIMO
Cooperation Document for: Discussion 1 Introduction
[0107] Cooperation between neighbouring sites in a LTE-A system
improves coverage for the cell edge users as well as total cell
throughput. In the LTE standard, such cooperation is limited and
does not involve scheduling, data sharing or channel state
information state exchange between the transmitters. There are
several proposals to adopt multi-site cooperation techniques in the
LTE-A standard [1-4]. In this contribution, we study different
cooperation scenarios and propose some solutions for further study
for possible exploiting in the LTE-A standard.
[0108] 2 Cooperation Scenarios
[0109] Different system setups allow for different cooperation
level. Data sharing, CSI sharing and antenna configuration are
among the aspects for consideration in multi-site cooperation.
Here, we study some aspects of the system that need to be
considered for each cooperation technique.
[0110] The cooperating sites may be located to the same cell or
located in different cells. With multi-cell cooperation as shown in
FIG. 8, all participating sites have access to backhaul and hence
allowing for data exchange and CSI exchange. However, this requires
a distributed scheduling mechanism that enables cooperation for
such cell edge users. See FIG. 8.
[0111] Same-site cooperation includes NB-relay and relay-relay
cooperation as well as distributed antenna setups. In these cases,
a centralized scheduler is possible. However, for the case of
relays, a mechanism to share data and CSI between the nodes is open
for study. See FIGS. 9 and 10.
[0112] Antenna setup at the participating sites dictates the
available cooperation solutions. With an array antenna,
beam-forming solutions are possible, while for sites with MIMO
antenna setup, cooperation solutions need to extend the LTE-A
precoding schemes to multi-site scenarios.
[0113] Moreover, it is quite possible that for NB-relay and NB-home
NB cooperation, the cooperating sites have different antenna
setup.
[0114] Data and CSI sharing possibility allows for more advanced
cooperation techniques. In the NB-NB cooperation, the backhaul
latency may limit the cooperation, while in the relay cooperation
scenarios, the dominant factor in data and CSIT sharing is
overhead.
[0115] RS overhead and channel estimation complexity is another
aspect to study. While superposition dedicated RS for some
solutions maintain the RS overhead and complexity, some solutions
require separate channel estimation from different sites for
demodulation and/or precoder selection.
[0116] 3 Cooperation Solutions
[0117] Based on the attributes of the cooperating sites, different
multi-site cooperation levels are possible. Based on the CSI
knowledge at the transmitter, we can generalize the multi-site
solutions into three main categories. Open loop, closed loop and
semi closed cooperation techniques.
[0118] 3.1 Open Loop Cooperation Schemes
[0119] An open loop cooperation scheme use all the antenna ports at
the cooperating sites to maximize the transmit diversity or
throughput of the user. In OL cooperation, none of the cooperating
sites have access to channel state information and thus, rely on
multi-site and/or transmit diversity. For high geometry users,
different sites transmit independent data streams to enhance the
user experience. These techniques need independent channel
estimation from all cooperating sites. Moreover, for the transmit
diversity solutions, full data sharing is required.
[0120] 3.1.1 Band Switching Transmit Diversity
[0121] To improve the coverage to the cell edge users, the two (or
more) sites specify different bands to the user. The other sites
either keep quiet in the specified bands from other sites or send
low power data to their own cell centre users. Within the sub-band
allocated to each user, a single-site open loop scheme is utilized.
The main difference between this technique and FFR is that this
technique is enabled through scheduling. Also, to achieve
multi-site diversity, the transmitted data from all the sites
should come from the same codebook. Without data sharing, there is
no multi-site diversity gain and the only remaining gain is
interference avoidance.
[0122] Band switching transmit diversity is robust against small
timing and frequency mismatch between the cooperating sites.
However, it achieves the least possible diversity gain.
[0123] 3.1.2 Tone Switching Transmit Diversity
[0124] This technique is similar to band switching transmit
diversity except that the tones from different sites are interlaced
along time or frequency direction. Therefore, it achieves higher
frequency diversity than the former one. However, it makes it more
susceptible to synchronization mismatch between the two sites.
Similar to other multi-site TxD schemes, the UE should estimate the
channel from all the sites. However, this method induces a coloured
noise to neighbouring (non-cooperating) cells.
[0125] 3.1.3 Space-Time/Frequency Transmit Diversity
[0126] Similar to single-site transmit diversity,
space-time/frequency block codes can achieve high diversity order
for all turbo coding rates. However, the total number of antennas
in the code increases with the increase in the number of
cooperating sites. Hence, bigger S-T/F codes are required. One
solution is to reuse the existing transmit diversity schemes and
combine single-site S-T/F codes with tone switching similar to the
TxD scheme in LTE 4-Tx transmit diversity scheme. Space-tone
cooperation between the sites maintains the spectral density of the
interference to the neighbouring cells.
[0127] 3.1.4 Multi-Site Spatial Multiplexing
[0128] For UEs with high geometry from more than one site, spatial
multiplexing improves the user throughput and also total sector
throughput. With multi-site spatial multiplexing, each site sends
its own data and there is no need to exchange data between the
sites. Moreover, by exploiting a SIC receiver, the total throughput
can be further improved. Similar to multi-site TxD schemes,
(ignoring the frequency selectivity of channel) the interference to
other sites remain white.
[0129] 3.2 Closed Loop Cooperation Schemes
[0130] With access to the channel state information, closed loop
cooperation is available between the sites. Depending on the CSI
knowledge type, its accuracy and how much this information is
shared between the sites, different cooperation solutions are
possible. For TDD systems, the uplink sounding channel provides
access to the DL channel coefficients, For FFD systems, this
information is collected by the user feedback or uplink AoA in
array sites. Although for the array sites, the beam-forming matrix
does not change fast even for moderate and high speed users, closed
loop cooperation between the sites is sensitive to UE movement and
hence is limited to fixed and low speed UEs.
[0131] 3.2.1 Multi-Site Beam-Forming
[0132] Sites with array antennas may use the uplink AoA information
for closed loop operation. When two array sites cooperate to send
the same data to the UE using beam-forming, a mechanism to ensure
constructive addition of the two beams is required. For this
purpose, a timing/distance adjustment as well as phase correction
is required. For demodulation purposes, the two sites can apply
superposition dedicated RS to maintain RS overhead and simple
decoding.
[0133] 3.2.1.1 Timing/Distance Adjustment
[0134] Timing mismatch between the cooperating sites as well as
different distance to the UE results in a mismatch between the
arrival times of the signal from different times. This timing
mismatch results in a linear phase over frequency. A mechanism to
estimate the timing error and correcting it is required.
[0135] 3.2.1.2 Phase adjustment
[0136] After correcting the linear phase between the two beams, the
residual phase difference between the two sites needs to be
corrected. Unlike the beam-forming precoder which is constant over
frequency for each site, the phase difference may change over the
band due to residual timing mismatch and channel dispersion. The UE
may take one site as the reference and report the phase differences
to all other sites.
[0137] 3.2.2 Multi-Site Closed Loop Precoding
[0138] When two or more MIMO sites are cooperating, each site
applies precoders to the transmitted signal. Similar to multi-site
BF, the goal is to make the signal from all participating sites add
constructively at the receiver. Multi-site precoding is less
sensitive to timing/distance mismatch compared to the multi-site BF
because of the frequency selectivity nature of the precoder. Still,
timing adjustment should ensure a relatively constant phase from
all sites over the precoding report sub-band size.
[0139] 3.2.2.1 Individual Precoding Report
[0140] The UE may report individual precoding matrices to different
sites. This way, the codebook from single-site closed loop is
reused. Also, the codeword selection criteria remain the same.
However, a phase adjustment between different sites is required
similar to multi-site beam-forming.
[0141] 3.2.2.2 Aggregate Precoding Report
[0142] Here, the UE assumes that all the antennas from all the
ports are from the same site and find a precoder that best matches
the entire antenna set. The UE finds the precoding matrix using a
bigger precoder codebook. Each site uses a portion of the precoding
matrix corresponding to its antenna ports for transmitting data to
the user. By using only one PMI, there is no need for phase
adjustment between the sites.
[0143] 3.2.3 Closed Loop Cooperation Between Array and MIMO
Sites
[0144] The aforementioned techniques for multi-site cooperation can
be extended to cooperation between array and MIMO sites.
[0145] 3.3 Semi closed loop cooperation techniques
[0146] As mentioned before, closed loop cooperation techniques are
sensitive to UE movement, timing and phase mismatches. They also
require higher complexity and feedback overhead compared to
single-site closed loop schemes. Open loop cooperation between
sites each performing a closed loop transmission to the UE is a
reasonable compromise that maintains the feedback overhead and
complexity while benefiting from multi-site diversity and closed
loop gain. While semi closed loop techniques do not achieve the
full cooperation gain, they offer the following advantages. [0147]
Easier implementation by reusing single site feedback signaling and
closed loop techniques [0148] No need for beam phase correction
[0149] No need for fine timing/distance adjustment [0150]
Facilitate cooperation between MIMO and array sites [0151] More
robust against channel aging [0152] Channel coefficients from the
same site age in the same way especially with LoS or array antennas
[0153] More robust against carrier frequency synchronization
errors
[0154] 3.3.1 Multi-Site Beam-Forming Transmit Diversity
[0155] Two or more array sites can cooperate to use a transmit
diversity scheme (like the Alamouti code) to send the same data
stream to the UE. A coarse timing adjustment is enough for
beam-forming transmit diversity and no phase correction is
required. The drawback of this method is that the UE needs
orthogonal dedicated RS from different sites as independent channel
estimation from different sites is needed.
[0156] 3.3.2 Multi-Site Closed Loop Transmit Diversity
[0157] Similar to multi-site beam-forming transmit diversity, two
or more MIMO sites use a space-time code to transmit data to the
UE. Again, the sensitivity to timing errors is very low and there
is no need for phase adjustment. The system can reuse the
single-site closed loop methods.
[0158] 3.3.3 Multi-Site Closed-Loop/Beam-Forming SM
[0159] Similar to open loop multi-site spatial multiplexing, for
high geometry UEs, the cooperating sites send independent data
streams to the UE. The UE reports individual precoders to the
cooperating sites in the MIMO case. For array antenna setup, the UL
AoA information is used for BF purposes. The precoder selection
criteria can include minimizing inter-layer interference between
different sires.
[0160] 3.4 Multi-Site Multi-User Cooperatin
[0161] Multi-site single user cooperation improves user throughput
and coverage at the expense of lower frequency reuse factor. If two
(or more) UEs are in the coverage area of the same two (or more)
sites, multi-site multi-user cooperation can improve the user
experience while benefiting from multi-user techniques to improve
total cell throughput.
[0162] Interference alignment technique (also called as X-MIMO) can
reduce the interference dimension at the users and hence, increase
the total number of layers transmitted to the users [5].
SUMMARY
[0163] In this contribution, we provided some study points for the
cooperation scenarios between different sites and provided some
solutions for further study to be adopted by the LTE-A standard. We
studied the cooperation in three categories: open loop, closed loop
and semi-closed loop. Backhaul overhead to share data and CSI, RS
overhead, feedback overhead, complexity and sensitivity to timing
error, distance and phase mismatch are among parameters that need
to be addressed for different cooperation solutions.
[0164] Table 1 provides some details on the requirements on
different algorithms and their expected gain.
TABLE-US-00002 TABLE 1 Cooperation solutions and requirements RS
for Demodulation precoder Data CSI at Scheme RS selection Exchange
transmitter Antenna setup Note on gain Band switching Orthogonal NA
None or None Both Interference transmit full for avoidance +
diversity Multi-site frequency diversity selective scheduling Tone
switching Orthogonal NA None or None Both Interference transmit
full for avoidance + diversity Multi-site frequency diversity
diversity Space/Tone Orthogonal NA Full None Both Spatial transmit
diversity diversity OL SM Orthogonal NA None None Both High
throughput + SIC Multi-site BF Superposition NA Full AoA + phase
Array BF gain dedicated correction Multi-site CL Superposition
orthogonal Full Individual MIMO CL gain (individual dedicated or
common precoder Precoder) orthogonal report + common phase
correction + timing adjustment Multi-site CL Superposition
orthogonal Full Collective MIMO CL gain (May (aggregate dedicated
or common precoder + need bigger Precoder) orthogonal timing
precoder set) common adjustment Heterogeneous Superposition
orthogonal Full AoA (array) + Heterogeneous BF and CL multi-site
dedicated common precoder gain CL/BF (MIMO) + phase correction +
timing adjustment Multi-site CL orthogonal orthogonal Full
Individual MIMO Multi-site TxD dedicated or common precoder
diversity + CL orthogonal (maximize gain common per site power)
Multi-site CL orthogonal NA Full AoA Array Multi-site TxD dedicated
diversity + BF gain Multi-site orthogonal orthogonal Full
Individual Both Multi-site Heterogeneous dedicated or common
precoder + diversity + CL TxD orthogonal AoA gain + BF common gain
Multi-site BF Orthogonal NA None AoA Array High SM dedicated
throughput + SIC Multi-site closed orthogonal orthogonal None
Individual MIMO High loop SM dedicated or common precoder
Throughput + orthogonal (minimize SIC common interference)
Heterogeneous Orthogonal orthogonal None AoA (array) +
Heterogeneous High multi-site SM dedicated or common precoder
throughput + common (MIMO) SIC X-MIMO Orthogonal orthogonal Partial
Channel MIMO Interference dedicated or common coefficients
alignment + orthogonal high common throughput + SIC
REFERENCES
[0165] [1] Alcatel Shanghai Bell, Alcatel-Lucent, "DL Collaborative
MIMO for LTE-A," R1-082812, 3GPP TSG RANI #54, Jeju, Korea, Aug.
18-22, 2008.
[0166] [2] Samsung, "Inter-Cell Interference Mitigation through
Limited Coordination," R1-082886, 3GPP TSG RANI #54, Jeju, Korea,
Aug. 18-22, 2008.
[0167] [3] Ericsson, "LTE-Advanced--Coordinated Multipoint
transmission/reception," R1-083069, 3GPP TSG RANI #54, Jeju, Korea,
Aug. 18-22, 2008.
[0168] [4] LG Electronics, "Network MIMO in LTE-Advanced,"
R1-082942, 3GPP TSG RANI #54, Jeju, Korea, Aug. 18-22, 2008.
[0169] [5] M. A. Maddah-Ali, A. S. Motahari, A. K. Khandani,
"Communication over MIMO X Channels: Interference Alignment,
Decomposition, and Performance Analysis," IEEE Trans. on
Information Theory, Volume 54, August 2008, pp. 3457-3470.
[0170] Wireless Systems with Multi-Transmitters and Multi-Receivers
Background
[0171] Conventionally, in wireless systems, one of the following
configurations has been employed: [0172] Some transmitters send
data to only one of the receiver (e.g. Uplink Channel, Multi-access
channel)--See FIG. 11, [0173] Some receivers receive data only from
one transmitter (e.g. Downlink Channel, Broadcast Channel)--See
FIG. 12. [0174] Each receiver receives data from one of the
intended transmitters (e.g. Interference Channels)--See FIG.
13.
[0175] Proposed Scheme
[0176] Here, we propose a new scenario of communication in which in
a system with multiple transmitters and receivers (see FIG. 14,
wherein in .DELTA.T.sub.1 time slot and in .DELTA.F.sub.1
bandwidth, we have one configuration, while in .DELTA.T.sub.2 time
slot and in .DELTA.F.sub.2 bandwidth, we have another
configuration) [0177] Each transmitter transmits data to several
receivers. [0178] Each receiver receives data from several
transmitters. [0179] The transmission can be done at the same time
slot and same frequency bandwidth [0180] In each bandwidth and time
slot, the configuration of communication may be different from the
configuration of the other bandwidth and time slot. [0181] Signals
transmitted in different time and different frequencies can be
dependent or independent
[0182] Example: In the system shown in FIG. 14, we have, [0183] 6
nodes [0184] In .DELTA. T.sub.1 time slot and in .DELTA. F.sub.1
bandwidth, [0185] Node 1 sends data to nodes 3 and 4 [0186] Node 2
sends data to nodes 3, 4,5 and 6 [0187] Node 3 receives data from
nodes 1 and 2 [0188] Node 4 receives data from nodes 1 and 2 [0189]
Nodes 5 and 6 receive data only from node 2 [0190] Signal
transmitted by nodes one and two can be dependent or independent
[0191] In .DELTA. T.sub.2 time slot and in .DELTA. F.sub.2
bandwidth, [0192] Node 1 sends data to nodes 3 and 5 [0193] Node 2
sends data to nodes 3 and 5. [0194] Node 6 sends data to nodes 3,
4, and 5. [0195] Node 3 receives data from nodes 1, 2, and 6.
[0196] Node 4 receives data from nodes 1 and 6. [0197] Nodes 5
receives data from nodes 1, 2, and 6. [0198] Signal of the nodes
1,2, and 6 can be dependent or independent [0199] Signals of the
nodes 1 and 2 in .DELTA. T.sub.1 time slot and in .DELTA. F.sub.1
bandwidth and signals of the nodes 1,2, and 6 in .DELTA.T.sub.2
time slot and in .DELTA.F.sub.2 bandwidth can be dependent or
independent.
EXAMPLE
[0200] Multi-Antenna Systems
[0201] As an example of the proposed scheme, the following scenario
has been detailed:
[0202] Multiple-Antenna System with Two Transmitters and Two
Receivers:
[0203] We consider a MIMO system with two transmitters and two
receivers, where [0204] Transmitter t, t=1; 2, is equipped with
m.sub.t antennas [0205] Receiver r, r=1, 2, is equipped with
n.sub.r antennas. [0206] The channel between transmitter t and
receiver r is represented by the channel matrix H.sub.rt, where
H.sub.rt is a n.sub.r by m.sub.t matrix. The received vector
y.sub.r by receiver r, r=1; 2, is given by,
[0206] y.sub.1=H.sub.11s.sub.1+H.sub.12s.sub.2+w.sub.1 (Eq 1)
y.sub.2=H.sub.21s.sub.1+H.sub.22s.sub.2+w.sub.2 (Eq 2)
[0207] where [0208] s.sub.t represents the transmitted vector by
transmitter t [0209] w.sub.r is noise vector at receiver r [0210]
y.sub.r is the received vector at receiver r
[0211] In this system (see FIG. 15), [0212] Transmitter 1 sends
b.sub.11 data streams to receiver one and b.sub.21 data streams to
receiver two [0213] Transmitter 2 sends b.sub.12 data streams to
receiver one and b.sub.22 data streams to receiver two. [0214]
Transmitters one and two cooperate to send b.sub.1c data streams to
receiver one. [0215] Transmitters one and two cooperate to send
b.sub.2c data streams to receiver two. [0216] The six sets of data
streams can be dependent or independent.
EXAMPLE
[0217] ZF Scheme
[0218] This scheme can be utilized in many applications [0219]
Example: Using multiple relays in downlink (see FIG. 16) [0220]
Example: Using multiple relays in uplink (see FIG. 17) [0221]
Example: Using multiple relays for interference links (See FIG.
18)
[0222] To modulate or demodulate the data streams, any linear or
non-linear scheme can be applied.
[0223] Numbers b.sub.rt and b.sub.rc can be selected based on
design requirements.
[0224] As an example, we investigate a scheme based on [0225] ZF
linear pre-preprocessing and post- processing such that the data
streams have no interference over each other
[0226] In this example, we assume that
n.sub.1=n.sub.2=m.sub.1=m.sub.2=m.
[0227] In this example (See FIG. 19)
s.sub.1=V.sub.11d.sub.11+V.sub.12d.sub.12+V.sub.1c.sub.--.sub.1d.sub.1c+-
V.sub.2c.sub.--.sub.1d.sub.2c (Eq 3)
s.sub.2=V.sub.12d.sub.12+V.sub.22d.sub.22+V.sub.1c.sub.--.sub.2d.sub.1c+-
V.sub.2c.sub.--.sub.2d.sub.2c (Eq 4)
[0228] Where [0229] d.sub.rt is a b.sub.rt dimensional vector, r,
t=1,2, which include b.sub.rt data streams [0230] d.sub.1c is a
b.sub.1c dimensional vector, r=1,2, which include b.sub.1c data
streams [0231] d.sub.2c is a b.sub.2c dimensional vector, r=1,2,
which include b.sub.2c data streams [0232] V.sub.rt is a m times
b.sub.rt matrix, r, t=1, 2 which include b.sub.rt data stream
[0233] V.sub.1c.sub.--.sub.1 and V.sub.1c.sub.--.sub.2 are m times
b.sub.1c matrices [0234] V.sub.2c.sub.--.sub.1 and
V.sub.2c.sub.--.sub.2 are m times b.sub.2c matrices [0235] To
decode d.sub.rt, the received vector y.sub.r is passed through a
filter U.sub.rtQ.sub.r [0236] To decode d.sub.1c, the received
vector y.sub.1 is passed through a filter U.sub.1cQ.sub.1 [0237] To
decode d.sub.2c, the received vector y.sub.2 is passed through a
filter U.sub.2cQ.sub.2
[0238] In what follows, the design steps to select system parameter
is explained.
[0239] Design Steps:
[0240] Step 1: Choosing Integers b.sub.rt, r,t=1,2 and b.sub.rc,
r=1,2 [0241] Select integers b.sub.rt, r,t=1,2 and b.sub.rc, r=1,2,
such that the following constraints satisfy:
[0241] b1c: b.sub.1c+b.sub.2c+b.sub.22+b.sub.21<=2m (Eq 5)
b2c: b.sub.1c+b.sub.2c+b.sub.11+b.sub.12<=2m (Eq 6)
b11: b.sub.11+b.sub.2c+b.sub.22+b.sub.21<=m (Eq 7)
b12: b.sub.12+b.sub.2c+b.sub.22+b.sub.21<=m (Eq 8)
b21: b.sub.21+b.sub.1c+b.sub.11+b.sub.12<=m (Eq 9)
b22:b.sub.22+b.sub.1c+b.sub.11+b.sub.12<=m (Eq 10)
b.sub.11+b.sub.21+b.sub.1c<=m (Eq 11)
b.sub.11+b.sub.21+b.sub.2c<=m (Eq 12)
b.sub.12+b.sub.22+b.sub.1c<=m (Eq 13)
b.sub.12+b.sub.22+b.sub.1c<=m (Eq 14)
b.sub.11b.sub.12+b.sub.21+b.sub.22+b.sub.1c+b.sub.2c<=2m (Eq 15)
[0242] Remark: Each of the first four inequalities corresponds to
one of the parameters b.sub.rt, b.sub.rc, r, t=1, 2, in the sense
that if b.sub.rt, or b.sub.rc r, t=1;2, is zero, the corresponding
inequality is removed from the set of constraints. [0243] Remark:
Based on the application, some new constraint may be added to the
system [0244] Remark: If in an application, we are not interested
in common messages, we can choose b.sub.1c and b.sub.2c as
zero.
[0245] Step 2: Choosing Matrices Q1 and Q2 [0246] Choose matrix
Q.sub.1 as an (b.sub.1c+b.sub.11+b.sub.12) times m arbitrary
matrix. Similarly, choose matrix Q2 as an
(b.sub.2c+b.sub.21+b.sub.22) times in arbitrary matrix. [0247]
Remark: Q.sub.1 and Q.sub.2 can be chosen based on any optimization
criteria.
[0248] Step 3: Choosing Modulation Matrices: [0249] Select
modulation matrix V.sub.11 such that columns of V.sub.11 span null
spaces of Q.sub.2H.sub.21. [0250] Select Modulation matrix V.sub.21
such that columns of V.sub.21 span null spaces of Q.sub.1H.sub.11.
[0251] Select modulation matrix V.sub.12 such that columns of
V.sub.12 span null spaces of Q.sub.2H.sub.22. [0252] Select
modulation matrix V.sub.22 such that columns of V.sub.22 span null
spaces of Q.sub.1H.sub.12. [0253] Select modulation matrices
V.sub.1c.sub.--.sub.1 and V.sub.1c.sub.--.sub.2 such that columns
of [(V.sub.1c.sub.--.sub.1).sup.T,
(V.sub.1c.sub.--.sub.2).sup.T].sup.T span null space of the
[(Q.sub.2H.sub.21).sup.T, (Q.sub.2H.sub.22).sup.T].sup.T. [0254]
Select modulation matrices V.sub.2c.sub.--.sub.1 and
V.sub.2c.sub.--.sub.2 such that columns of
[(V.sub.2c.sub.--1).sup.T, (V.sub.2c.sub.--.sub.2).sup.T].sup.T
span null space of the [(Q.sub.1H.sub.12).sup.T,
(Q.sub.1H.sub.11).sup.T].sup.T.
[0255] Step 4: Choosing Demodulation Matrices: [0256] U.sub.11 is
selected such that the columns of U.sub.11 is orthogonal to the
columns of Q.sub.1H.sub.12V.sub.12 and Q.sub.1[H.sub.11 H.sub.12]
[(V.sub.1c.sub.--.sub.1).sup.T,
(V.sub.1c.sub.--.sub.2).sup.T].sup.T. [0257] U.sub.12 is selected
such that the columns of U.sub.12 is orthogonal to the columns of
Q.sub.1H.sub.11V.sub.11 and Q.sub.1[H.sub.11 H.sub.12]
[(V.sub.1c.sub.--.sub.1).sup.T,
(V.sub.1c.sub.--.sub.2).sup.T].sup.T. [0258] U.sub.1c is selected
such that the columns of U.sub.1c is orthogonal to the columns of
Q.sub.1H.sub.11V.sub.11 Q.sub.1H.sub.12V.sub.12. [0259] U.sub.21 is
selected such that the columns of U.sub.21 is orthogonal to the
columns of Q.sub.2H.sub.22V.sub.22 and Q.sub.2[H.sub.21 H.sub.22]
[(V.sub.2c.sub.--.sub.1).sup.T,
(V.sub.2c.sub.--.sub.2).sup.T].sup.T. [0260] U.sub.22 is selected
such that the columns of U.sub.22 is orthogonal to the columns of
Q.sub.2H.sub.21V.sub.21 and Q.sub.2[H.sub.21 H.sub.22]
[(V.sub.2c.sub.--.sub.1).sup.T,
(V.sub.2c.sub.--.sub.2).sup.T].sup.T. [0261] U.sub.2c is selected
such that the columns of U.sub.2c is orthogonal to the columns of
Q.sub.2H.sub.21V.sub.21 and Q.sub.2H.sub.22V.sub.22.
[0262] Remark: Equations (Eq 5) to (Eq 15) guarantee that we can
design such transmit and receive filters.
[0263] Remark: The above steps are based on nulling the
interference of data streams over each other. Other linear or
nonlinear schemes like MMSE scheme, successive decoding,
dirty-paper-coding, etc. can be used instead of zero-forcing
filters.
EXAMPLE
[0264] ZF Scheme with Frequency Extension
[0265] In the above scheme, we assume that each node has m
antennas, providing m space dimensions. Apparently, it is possible
to provide dimensions using time and frequency resources. In what
follows, as an example, we extend the above example to the case,
where J frequency sub-bands are also available.
[0266] Multiple-Antenna System with Two Transmitters and Two
Receivers and J sub-bands
[0267] Transmitter t, t=1; 2, is equipped with m.sub.t antennas
[0268] Receiver r, r=1, 2, is equipped with n.sub.r antennas.
[0269] The channel between transmitter t and receiver r is at
sub-band j, j=1, . . . ,J, represented by the channel matrix
H.sub.rt(j), where H.sub.rt (j) is a n.sub.r by m.sub.t complex
matrix. The received vector y.sub.r(j) by receiver r, r=1; 2, is
given by,
y.sub.1(j)=H.sub.11(j)s.sub.1(j)+H.sub.12(j) s.sub.2(j)+w.sub.1(j)
(Eq 16)
y.sub.2(j)=H.sub.21(j)s.sub.1(j)+H.sub.22(j)s.sub.2(j)+w.sub.2(j)
(Eq 17)
[0270] where
[0271] s.sub.t(j) represents the transmitted vector by transmitter
t at frequency sub-band j
[0272] w.sub.r(j) is noise vector at receiver r at frequency
sub-band j
[0273] y.sub.r(j) is the received vector at receiver r at frequency
sub-band j
[0274] We define H.sub.rt, s.sub.r, and y.sub.r as follows:
H rt = [ H rt ( 1 ) 0 0 0 0 H rt ( 2 ) 0 0 0 0 0 0 0 0 H rt ( J ) ]
, s t = [ s t ( 1 ) s t s t ( J ) ] y r = [ y r ( 1 ) y r ( 1 ) y r
( J ) ] r , t = 1 , 2 ##EQU00001## [0275] As an example, here again
we use ZF filter desing [0276] In this example we assume that
n.sub.1=n.sub.2=m.sub.1=m2=m. [0277] In this example,
[0277]
s.sub.1=V.sub.11d.sub.11+V.sub.12d.sub.12+V.sub.1c.sub.--1d.sub.1-
c+V.sub.2c.sub.--1d.sub.2c (eq 18)
s.sub.2=V.sub.12d.sub.12+V.sub.22d.sub.22+V.sub.1c.sub.--2d.sub.1c+V.sub-
.2c.sub.--2d.sub.2c (Eq 19)
[0278] Where [0279] d.sub.rt is a b.sub.rt dimensional vector,
r,t=1,2, which include b.sub.rt data streams [0280] d.sub.1c is a
b.sub.1c dimensional vector, r=1,2, which include b.sub.1c data
streams [0281] d.sub.2c is a b.sub.2c dimensional vector, r=1,2,
which include b.sub.2c data streams [0282] V.sub.rt is a m times
b.sub.rt matrix, r,t=1,2 which include b.sub.rt data stream [0283]
V.sub.1c.sub.--1 and V.sub.1c.sub.--.sub.2 are J.m times b.sub.1c
matrices [0284] V.sub.2c.sub.--1 and V.sub.2c.sub.--.sub.2 are J.m
times b.sub.2c matrices [0285] To decode d.sub.rt, the received
vector y.sub.r is passed through a filter U.sub.rtQ.sub.r [0286] To
decode d.sub.1c, the received vector y.sub.1 is passed through a
filter U.sub.1cQ.sub.1 [0287] To decode d.sub.2c, the received
vector y.sub.2 is passed through a filter U.sub.2cQ.sub.2
[0288] Design Steps:
[0289] Step 1: Choosing Integers brt, r,t=1,2 and brc, r=1,2 [0290]
Select integers brt, r,t=1,2 and brc, r=1,2, such that the
following constraints satisfy:
[0290] b1c: b.sub.1c+b.sub.2c+b.sub.22+b.sub.21<=2J.m (Eq
20)
b2c: b.sub.1c+b.sub.2c+b.sub.11+b.sub.12<=2J.m (Eq 21)
b11: b.sub.11+b.sub.2c+b.sub.22+b.sub.21<=J.m (Eq 22)
b12: b.sub.12+b.sub.2c+b.sub.22+b.sub.21<=J.m (Eq 23)
b21: b.sub.21+b.sub.1c+b.sub.11+b.sub.12<=J.m (Eq 24)
b22:b.sub.22+b.sub.1c+b.sub.11+b.sub.12<=J.m (Eq 25)
b.sub.11+b.sub.21+b.sub.1c<=J.m (Eq 26)
b.sub.11+b.sub.21+b.sub.2c<=J.m (Eq 27)
b.sub.12+b.sub.22+b.sub.1c<=J.m (Eq 28)
b.sub.12+b.sub.22+b.sub.1c<=J.m (Eq 29)
b.sub.11b.sub.12+b.sub.21+b.sub.22+b.sub.1c+b.sub.2c<=2J.m (Eq
30) [0291] Remark: Each of the first four inequalities corresponds
to one of the parameters b.sub.rt, b.sub.rc, r, t=1, 2 in the sense
that if b.sub.rt, or b.sub.rc r, t=1;2, is zero, the corresponding
inequality is removed from the set of constraints. [0292] Remark:
Based on the application of the proposed scheme, some new
constraint may be added to the system [0293] Remark: If based on
the application, we are not interested in common messages, we can
choose b.sub.1c and b.sub.2c as zero.
[0294] Step 2: Choosing matrices Q.sub.1 and Q.sub.2 [0295] choose
matrix Q.sub.1, as an (b.sub.1c+b.sub.11+b.sub.12) times in
arbitrary matrix. Similarly, choose matrix Q.sub.2 as an
(b.sub.2c+b.sub.21+b.sub.22) times In arbitrary matrix. [0296]
Remark: Q.sub.1 and Q.sub.2 can be chosen based on any optimizing
criteria
[0297] Step 3: Choosing Modulation Matrices: [0298] Select
modulation matrix V.sub.11 such that columns of V.sub.11 span null
spaces of Q.sub.2H.sub.21. [0299] Select Modulation matrix V.sub.21
such that columns of V.sub.21 span null spaces of Q.sub.1H.sub.11.
[0300] Select modulation matrix V.sub.12 such that columns of
V.sub.12 span null spaces of Q.sub.2H.sub.22. [0301] Select
modulation matrix V.sub.22 such that columns of V.sub.22 span null
spaces of Q.sub.1H.sub.12. [0302] Select modulation matrices
V.sub.1c.sub.--.sub.1 and V.sub.1c.sub.--.sub.2 such that columns
of [(V.sub.1c.sub.--1).sup.T, (V.sub.1c.sub.--.sub.2).sup.T].sup.T
span null space of the [(Q.sub.2H.sub.21).sup.T,
(Q.sub.2H.sub.22).sup.T].sup.T. [0303] Select modulation matrices
V.sub.2c.sub.--.sub.1 and V.sub.2c.sub.--2 such that columns of
[(V.sub.2c.sub.--.sub.1).sup.T,
(V.sub.2c.sub.--.sub.2).sup.T].sup.T span null space of the
[(Q.sub.1H.sub.12).sup.T, (Q.sub.1H.sub.11).sup.T].sup.T.
[0304] Step 4: Choosing Demodulation Matrices: [0305] U.sub.11 is
selected such that the columns of U.sub.11 is orthogonal to the
columns of Q.sub.1H.sub.12V.sub.12 and
Q.sub.1[H.sub.11H.sub.12][(V.sub.1c.sub.--.sub.1).sup.T,(V.sub.1c.sub.--.-
sub.2).sup.T].sup.T. [0306] U.sub.12 is selected such that the
columns of U.sub.12 is orthogonal to the columns of
Q.sub.1H.sub.11V.sub.11 and
Q.sub.1[H.sub.11H.sub.12][(V.sub.1c.sub.--.sub.1).sup.T,(V.sub.1c.sub.--.-
sub.2).sup.T].sup.T. [0307] U.sub.1c is selected such that the
columns of U.sub.1c is orthogonal to the columns of
Q.sub.1H.sub.11V.sub.11 and Q.sub.1H.sub.12V.sub.12. [0308]
U.sub.21 is selected such that the columns of U.sub.21 is
orthogonal to the columns of Q.sub.2H.sub.22V.sub.22 and
Q.sub.2[H.sub.21H.sub.22][(V.sub.2c.sub.--.sub.1).sup.T,(V.sub.2c.sub.--.-
sub.2).sup.T].sup.T. [0309] U.sub.22 is selected such that the
columns of U.sub.22 is orthogonal to the columns of
Q.sub.2H.sub.21V.sub.21 and
Q.sub.2[H.sub.21H.sub.22][(V.sub.2c.sub.--.sub.1).sup.T,(V.sub.2c.sub.--.-
sub.2).sup.T].sup.T. [0310] U.sub.2c is selected such that the
columns of U.sub.2c is orthogonal to the columns of
Q.sub.2H.sub.21V.sub.21 and Q.sub.2H.sub.22V.sub.22. [0311] Remark:
Remark: (Eq 20) to (Eq 30) guarantee that we can design such
transmit and receive filters.
[0312] Advantage of the Proposed Scheme [0313] One show the
advantage of the proposed scenario, we consider a downlink system
with [0314] One base station with 8 antennas (or 8 available
dimensions) [0315] Two relays each with 4 antennas [0316] To
receiver each with 4 antennas
[0317] Consider a period of time T.
[0318] In what follows, we evaluate three signaling schemes and
compare the overall rate achieved by each schemes.
[0319] Scheme One: Conventional Scheme
[0320] In time period [0, T/3], base station simultaneously sends
[0321] 4 data streams, intended for receiver one, to relay one
[0322] 4 data streams, intended for receiver two, to relay two
[0323] In time period [T/3,2T/3], relay one sends 4 data streams to
receiver one.
[0324] In time period [2T/3,T], relay two sends 4 data streams to
receiver two.
[0325] The overall throughput of this scheme is 8/3 log(P.sub.T),
where P.sub.T represents total power.
[0326] Remark: This is the best achievable rate with conventional
scheme.
[0327] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0328] Scheme Two: Proposed scheme where signals of the relays are
correlated
[0329] In time period [0,T/2], base station simultaneously sends
[0330] One data stream, intended to receiver one, to relay one,
[0331] One data stream, intended to receiver one, to relay two,
[0332] One data stream, intended to receiver two, to relay one,
[0333] One data stream, intended to receiver two, to relay two,
[0334] One data stream, intended to receiver one, to both relays,
[0335] One data stream, intended to receiver two, to both relays,
[0336] In time period [T/2,T], relays one and two, send data
simultaneously to receiver one and two, based on proposed scheme
with b.sub.11=b.sub.12=b.sub.21=b.sub.22=b.sub.1c=b.sub.2c=1.
[0337] The overall throughput of this scheme is 3 log(P.sub.T),
where P.sub.T represents total power.
[0338] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0339] Scheme Three: Proposed scheme where the signals of the
relays are uncorrelated
[0340] In time period [0,2T/5], base station simultaneously sends
[0341] Two data streams, intended to receiver one, to relay one,
[0342] Two data streams, intended to receiver one, to relay two,
[0343] Two data streams, intended to receiver two, to relay one,
[0344] Two data streams, intended to receiver two, to relay
two,
[0345] In time period [2T/5,T], relays one and two, send data
simultaneously to receiver one and two, based on proposed scheme in
with b.sub.11=b.sub.12=b.sub.21=b.sub.22=4, b.sub.1c=b.sub.2c=0,
and J=3.
[0346] The overall throughput of this scheme is 16/5 log(P.sub.T),
where P.sub.T represents total power.
[0347] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0348] It is clear from this example that scheme two and three
which are based on the proposed scheme perform better than
conventional schemes.
[0349] Key Features
[0350] The proposed scenario of Communication improves the
performance of the communication systems in terms of overall
throughput, reliability, and coverage.
[0351] To design such system, we can use any linear or non-linear
filters based on the design requirements.
[0352] The ZF scheme, presented in detail, can be applied simply to
improve the performance of the communication system.
[0353] The ZF scheme, presented here, can be generalized to any
number of transmitters and receivers, to support any number of
transmitters and receivers.
[0354] The processing, designed based on ZF scheme, can be employed
and redesigned based on other known scheme such as dirty-paper
coding, successive decoding, MMSE filters, etc.
[0355] The communication schemes shown in FIG. 16 (uplink system
with parallel relays), FIG. 17 (downlink system with parallel
relays), and FIG. 18 (Interference channel with parallel relays)
are helpful in wireless communication systems. This configurations
can be generalized to support any number of transmitters, relays,
and receivers. At relay nodes, any scheme such as
decode-and-forward. Amplify-and-forward, etc, can be employed.
X-MIMO Systems with Multi-Transmitters and Multi-Receivers
[0356] Brief Description of the Gist of the Application
[0357] This Application provides a solution for MP-to-MP MIMO
systems to increase the spectral efficiency by coordinating the
interference.
[0358] The interference arriving at each receive node is
coordinated on the same subspace, so the signal subspace is
expanded->higher number of streams. [0359] Method
requirements/procedure [0360] Each transmitter has the knowledge of
its MIMO channel information. [0361] No data-exchanging required
between the transmitters, and no data-exchanging in the receiver
side (non cooperative transmission/reception).
[0362] Brief Statement of the Value to Nortel of the
Application
[0363] The basic scheme of X-MIMO can be generalized to many
wireless application, such as multi-hop relay, distributed MIMO
networking.
[0364] Previous Art: [0365] Network MIMO: using an additional
backbone system to connect transmitters or receivers which enable
us to apply advance schemes such as dirty paper precoding. [0366]
Requires data exchange between transmitters. [0367] Using more
transmit/receive antennas for a given number of data streams.
[0368] X-MIMO Basic Elements
[0369] Each transmitter sends the pilot for each antenna and the
pilot for each transmitter is orthogonal.
[0370] Each receiver estimates all the incoming MIMO channels
[0371] It computes the specific receive filters and feeds back the
compound filter and MIMO channel to a specific transmitter.
[0372] Each transmitter computes the linear pre-coding filter based
on such feedback information from the receiver. [0373] Each
transmitter sends the pre-coded data. [0374] Each receiver
demodulates the corresponding data from filtered receive signal
[0375] Identify the Products in which the Application may be
Used
[0376] This Application can be used as Nortel-specific proprietary
implementation. [0377] Enterprise solution. [0378] Wireless
backhaul
[0379] It can be standardized in the next generation broadband
wireless standards. [0380] Nomadic multi-user soft handoff [0381]
BS/Relay Cooperation
[0382] List of Key Features
[0383] This method enables the X-MIMO channels to minimize the
dimensions of the interference.
[0384] It maximizes the number of communication streams over the
channel for a given number of antennas.
[0385] The processing can be employed and redesigned based on
different schemes such as dirty-paper coding, successive decoding,
MMSE filters, ZF, etc.
[0386] This method requires no data communication or CSI exchange
between transmitters.
[0387] The communication schemes such as uplink system with
parallel relays, downlink system with parallel relays and
Interference channel with parallel relays are some examples of the
application of the proposed method in wireless systems and can be
generalized to support any number of transmitters, relays, and
receivers.
[0388] BACKUPS
[0389] Background [0390] Wireless system configurations. [0391] CL
MIMO [0392] CL Network MIMO
[0393] X-MIMO [0394] Examples of the advantages of the proposed
method
[0395] WIRELESS SYSTEM CONFIGURATIONS
[0396] Conventionally, in wireless systems, one of the following
configurations has been employed: [0397] One transmitter sends data
to one receiver. [0398] Some transmitters send data to only one of
the receiver (e.g. Uplink Channel, Multi-access channel). [0399]
Some receivers receive data only from one transmitter (e.g.
Downlink Channel, Broadcast Channel). [0400] Each receiver receives
data from one of the intended transmitters (e.g. Interference
Channels).
[0401] CL MIMO
[0402] See FIGS. 20 and 21.
[0403] Point-to-point: there is only one transmitter and one
receiver. [0404] The transmitter selects a precoder based on the
channel. [0405] Requires channel knowledge at the transmitter.
[0406] The maximum number of streams is min(nTx,nRx)
[0407] Point-to-multipoint: there is only one transmitter but a few
receivers. [0408] The transmitter selects a precoder based on the
compound channel. [0409] The goal is to minimize the interference
among receivers. [0410] Requires channel knowledge at the
transmitter. [0411] The maximum total number of streams is
min(nTx,InRx)
[0412] CL NETWORK MIMO
[0413] Multiple transmitters and multiple receivers.
[0414] Transmitters communicate over a backbone and exchange data
and/or CSI
[0415] The maximum total number of streams is
min(.SIGMA.nTx,.SIGMA.nRx)
[0416] X-MIMO
[0417] Here, we propose a new scenario of communication in which in
a system with multiple transmitters and receivers [0418] Each
transmitter transmits data to several receivers, [0419] Each
receiver receives data from several transmitters, [0420] The
transmission can be done at the same time slot and same frequency
bandwidth [0421] In each bandwidth and time slot, the configuration
of communication may be different from the configuration of the
other bandwidth and time slot. [0422] Signals transmitted in
different time and different frequencies can be dependent or
independent
EXAMPLE
[0423] Two transmitters and two receivers close to each other
(strong interference). [0424] The total number of layers with the
conventional method is 3. [0425] 2-layers for link 1 and 1-layer
for link 2 (or vice versa) [0426] Receiver one cancels one layer
and decodes two layers. [0427] Receiver two cancels two layers and
decodes one layer. [0428] With proposed method and using ZF, the
total number of layers are 4. [0429] Each transmitter sends a layer
to receiver one and one layer to receiver 2. [0430] Each decoder
cancels two layers of coordinated interference and decodes two
layers. [0431] The two interferences at each node are coordinated,
seen as only one interference stream.
[0432] Advantage of the Proposed Scheme (Example)
[0433] Consider a downlink system with [0434] One base station with
8 antennas (or 8 available dimensions) [0435] Two relays each with
4 antennas [0436] To receiver each with 4 antennas
[0437] Consider a period of time T
[0438] In what follows, we evaluate three signaling schemes and
compare the overall rate achieved by each schemes. See FIG. 22.
[0439] Scheme One: Conventional Scheme
[0440] In time period [0,T/3], base station simultaneously sends
[0441] 4 data streams, intended for receiver one, to relay one
[0442] 4 data streams, intended for receiver two, to relay two
[0443] In time period [T/3,2T/3], relay one sends 4 data streams to
receiver one.
[0444] In time period [2T/3,T], relay two sends 4 data streams to
receiver two.
[0445] The overall throughput of this scheme is 8/3 log(P.sub.T),
where P.sub.T represents total power.
[0446] Remark: This is the best achievable rate with conventional
scheme.
[0447] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0448] Scheme 2: X-Mimo with where Signals of the Relays are
Correlated
[0449] In time period [0,T/2], base station simultaneously sends
[0450] One data stream, intended to receiver one, to relay one,
[0451] One data stream, intended to receiver one, to relay two,
[0452] One data stream, intended to receiver two, to relay one,
[0453] One data stream, intended to receiver two, to relay two,
[0454] One data stream, intended to receiver one, to both relays,
[0455] One data stream, intended to receiver two, to both
relays,
[0456] In time period [T/2,T], relays one and two, send data
simultaneously to receiver one and two, based on proposed scheme
with b.sub.11=b.sub.12=b.sub.21=b.sub.22=b.sub.1c=b.sub.2c=1.
[0457] The overall throughput of this scheme is 3 log(P.sub.T),
where P.sub.T represents total power.
[0458] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0459] Scheme 2: X-Mimo with where Signals of the Relays are
Uncorrelated
[0460] In time period [0,2T/5], base station simultaneously sends
[0461] Two data streams, intended to receiver one, to relay one,
[0462] Two data streams, intended to receiver one, to relay two,
[0463] Two data streams, intended to receiver two, to relay one,
[0464] Two data streams, intended to receiver two, to relay
two,
[0465] In time period [2T/5,T], relays one and two, send data
simultaneously to receiver one and two, based on proposed scheme in
with b.sub.11=b.sub.12=b.sub.21=b.sub.22=4, b.sub.1c=b.sub.2c=0,
and J=3.
[0466] The overall throughput of this scheme is 16/5 log(P.sub.T),
where P.sub.T represents total power.
[0467] Remark: The overall incoming data streams by each relay is
the same as the overall outgoing data streams.
[0468] It is clear from this example that scheme two and three
which are based on the proposed scheme perform better than
conventional schemes.
* * * * *